This invention pertains to the hydrogenolysis of alditols such as sorbitol to produce glycerol and glycol products using a continuous fixed bed catalytic process.
The production of glycerol and polyols by hydrogenolysis of sorbitol has been widely studied. Generally, an optimum 30-40 W % of glycerol congeners has been reported in the product obtained from autoclave batch reaction processes. The reaction conditions used are high hydrogen partial pressure of 2000-5000 psig, temperature of 200.degree.-250.degree. C., (392.degree.-482.degree. F.), long residence time of 1.5 hours or more, and use of fine nickel powder catalyst of 100-200 mesh size in the form of a slurry with the feed.
A disclosure regarding hydrogenolysis of sorbitol is provided by Clark in Industrial & Engineering Chemistry, Vol. 50, No. 8 (August 1958), page 1125. Aqueous solution containing 40% of 99% D-sorbitol were used with 1% calcium hydroxide promotor and 50% nickel on kieselguhr catalyst suspended in a slurry with the feed in a stirred reactor. Conditions used were 2000-5600 psi hydrogen partial pressure, 215.degree.-245.degree. C. (419.degree.-473.degree. F.) temperature and reaction times up to 400 minutes (6.7 hrs) to produce glycerol, ethylene glycol, propylene glycol, and other more minor products.
U.S. Pat. No. 2,965,679 to Conradin discloses a similar process for producing glycerol and glycols from sugar alcohols using a suspended nickel on kieselguhr catalyst in an autoclave type reactor. Reaction conditions are 200.degree.-300.degree. C. temperature, 500-1000 atmospheric pressure and pH of 8-10, followed by filtration to remove catalyst and separation of the products.
Van Ling et al disclosed in Journal of Applied Chemistry, Vol. 19, pages 43-45, hydrogenation experiments using slurried catalyst in autoclave reactor on feeds of sucrose, glucose and fructose in methanol-water solution to produce glycerol. Catalyst used was CuO-CeO.sub.2 -SiO.sub.2 with 0-5% Ca(OH).sub.2 addition to the feed. Reaction conditions used were 200.degree.-250.degree. C. temperature, 100-300 atmospheric pressure and 10-120 minutes reaction time.
U.S. Pat. No. 3,471,580 to Hellwig et al discloses that by using a single or multi-stage upflow ebullated bed catalytic reactor at 200.degree.-550.degree. F. temperature and 700-3500 psia hydrogen partial pressure, glycerol and glycols can be produced from saccharides. Examples of the conditions used for converting a sorbitol type feed to glycerol in a single stage reaction were about 375.degree. F. temperature, 1700 psia hydrogen partial pressure, 1.2 liquid hourly space velocity (LHSV), and using nickel on alumina catalyst to produce roughly 50 W % glycerol and 20 W % propylene glycol, with the remainder being methanol, ethanol, isopropanol, and other products (col. 5, lines 40-53).
It is believed that none of these known processes are presently being used commercially to produce glycerol and related products on a continuous basis. Thus, further process improvements in alditol conversion for achieving continuous operations, reduced reaction conditions and increased glycerol product yields are desired, particularly using improved catalysts in fixed-bed reactors.